The present invention relates generally to ultrasonic devices and more specifically to an ultrasonic pneumotachometer.
In the medical field, it is often necessary to measure the respired gas volume in a person. This gas volume is obtained by measuring the velocity of gas flow, breath by breath, and integrating the velocity over a defined period of time.
There are many methods of measuring the gas velocity. One such method involves the use of a Fleisch type pneumotachometer (flowmeter) that was invented in the 1920""s. A Fleisch pneumotachometer includes a tube, two sets of screens to linearize the turbulent incoming gas flow to establish a region of laminar flow, and a pressure sensing transducer located between the screens. Since the pressure drop xcex94p is proportional to the gas velocity, the gas velocity can be determined by measuring xcex94p across the pressure sensing transducer. However, the Fleisch pneumotachometer works well only if the laminar regime is maintained. Turbulence causes xcex94p to vary nonlinearly with gas flow and thus affects the accuracy of the gas velocity determined using a Fleisch pneumotachometer. Accumulation of saliva and/or effluent inside the tube from the person""s lungs, particularly at the screens, will cause turbulence to occur. In general, to overcome the nonlinear effects, different diameter tubes are used to cover a range of up to 20 liters per second (1/sec).
Since the availability of lead titanate zirconate (PZT) piezoelectric material, ultrasonic flowmeters are now available, and are in common use for various applications. PZT is a piezoelectric material, which can be used to generate ultrasonic waves at different frequencies. In these pneumotachometers, the velocity of gas flow is determined by measuring the transit time of an ultrasound wave through a gas volume. However, accumulation of spit and other pulmonary effluents from a person""s lungs tend to block the wells in front of the transducers, making the pneumotachometer unreliable in those situations. Also, since such a pneumotachometer often uses small and single transducers, there is always a likelihood that the transducers could be totally blocked, causing the transducer to stop acquiring data. It would therefore be very beneficial to the art if the transducer output could be desensitized to such dropouts of the signal acquisition.
A solution, which would provide an accurate and reliable pneumotachometer for determining the velocity of a fluid flow, has been long sought but has eluded those skilled in the art.
The present invention provides an accurate and reliable pneumotachometer for determining the velocity of a fluid flow.
The present invention provides a pneumotachometer with annular ring transducers for determining the velocity of a fluid flow.
The present invention further provides a method for fabricating an annular ring transducer.
The present invention still further provides a novel and accurate flow measurement system as used with a pneumotachometer having annular ring transducers constructed in accordance with the present invention.
The above and additional advantages of the present invention will become apparent to those skilled in the art from a reading of the following detailed description when taken in conjunction with the accompanying drawings.